This is the first application filed for the present invention.
Not applicable.
The present invention relates to voltage converters and, in particular, to a dual-output voltage converter that provides a regulated low voltage output as well as an auxiliary high voltage output.
Many computer peripherals are powered from a single fixed DC voltage power supply and use step-down switching voltage regulators to supply lower voltages for driving logic circuits. A step-down switching voltage regulator, more commonly known in the art as a xe2x80x9cbuckxe2x80x9d converter, converts an applied input voltage to a lower output voltage. The output stage of a synchronous buck converter typically includes a pair of switches coupled in series across the input voltage supply. One switch, the voltage switch, is coupled to the voltage supply and the other switch is connected to ground. An output filter typically including an inductor and a capacitor is connected to a junction formed by the pair of switches. The capacitor is responsible for reducing the ripple content in voltage across it, whereas the inductor smoothes the current passing through it. The combined action of the LC filter, therefore, reduces the ripple content in the output voltage supplied to a load connected to the buck converter. Typically, feedback from the output of the LC filter is provided to a controller which drives the switches to connect the output filter to the voltage supply or to ground in order to maintain the output voltage at some predetermined low voltage level.
At the same time, however, some applications require a higher voltage than available from the voltage supply to power linear (analog) devices. In this respect, battery-powered equipment use DC/DC step-up converters to generate auxiliary supply voltages for internal circuits that require higher voltages than the available battery voltage. The conventional approach is to use either a switched capacitor voltage booster (i.e. charge pump) or an inductive step-up converter (also called boost converter). Boost converters have a high efficiency over the entire input voltage range. Charge pumps, on the other hand, provide a high efficiency over selected input voltage ranges. Since their design does not require any knowledge of magnetics, charge pumps are much easier to design and implement. In either case, however, such auxiliary high voltage generators usually require the use of a dedicated integrated circuit to provide the boosted voltages.
FIG. 1 illustrates a simplified schematic of a conventional voltage converter 10 used for providing a regulated low voltage output (RLVO) as well as an auxiliary high voltage output (AHVO) from a single applied DC input voltage VIN. The input voltage VIN is received at an input terminal 11 and supplied separately to a step-down or xe2x80x9cbuckxe2x80x9d integrated circuit voltage regulator VR1 and to a charge pump voltage doubler circuit VR2. The step-down integrated circuit voltage regulator VR1 includes a circuit block 12, which includes a pair of switches S1 and S2 connected in series between the input terminal 11 and ground. Control circuitry for driving the switches S1 and S2 is not shown but understood to be embodied by the circuit block 12. An output filter that includes an inductor L and a capacitor C is connected at the junction between the pair of switches S1 and S2. The junction between the inductor and capacitor of the output LC filter provides the regulated low voltage output (RLVO). A feedback path 14 is further provided from the output of the LC filter to the circuit block 12 to permit the control circuitry to appropriately drive the switches S1 and S2, so that a constant regulated low voltage output may be maintained.
The charge pump voltage doubler circuit VR2 includes a circuit block 16, which includes a pair of switches S3 and S4 connected in series between the input terminal 11 and ground. The associated control circuitry for driving the switches S3 and S4 is not illustrated but understood to be embodied within the circuit block 16. A first stage of the charge pump circuit VR2 includes a first diode D1 and a first capacitor C1. The input terminal 11 is connected via the first diode D1 to one electrode of the first capacitor while the other electrode of the first capacitor C1 is connected to a junction between the pair of switches S3 and S4 of the circuit block 16. A second stage of the charge pump circuit VR2 includes a second diode D2 and a second capacitor C2. A junction between the first diode D1 and first capacitor C1 is connected via the second diode D2 to one electrode of the second capacitor C2. The other electrode of the second capacitor C2 is connected to ground. The junction between the second diode D2 and second capacitor C2 of the charge pump circuit VR2 provides the auxiliary high voltage output (AHVO).
The step-down voltage regulator VR1 and charge pump VR2 depicted in FIG. 1 are standard circuit topologies whose operation is well known to those skilled in the art and, as such, will not be detailed.
As seen in FIG. 1, a dedicated switched-capacitor voltage booster or charge pump circuit VR2 is needed to provide an auxiliary high voltage output from the single input DC voltage VIN applied to the step-down voltage regulator VR1. Alternatively, an inductive booster may be employed. Either approach, however, requires the use of a dedicated integrated circuit with associated control circuitry to provide an auxiliary boosted voltage from a single applied DC input voltage. This leads to a high component count resulting in higher cost while preventing improvement in integration density.
It is therefore an object of the present invention to provide a voltage converter that integrates the functions of both a step-down voltage regulator and a charge pump into a single device.
A further object of the present invention is to provide a voltage converter capable of generating both a regulated low voltage output as well as an auxiliary high voltage output from a single applied input DC voltage.
Thus, an aspect of the present invention uses the inherent properties of a conventional step-down or xe2x80x9cbuckxe2x80x9d switching voltage regulator with a push-pull output stage to provide an auxiliary output voltage higher than the applied input voltage. Specifically, the push-pull output stage of the step-down voltage regulator is used to drive a charge pump voltage doubler circuit. Advantageously, the novel circuit topology of the present invention provides a low component (i.e. two diodes and two capacitors) count resulting in lower component cost and smaller physical size.